An image forming apparatus which is provided with an openable and closable discharge port on a conveyance path for discharging papers to an in-body tray when executing a print job, is known in the art. When the discharge port on the conveyance path is opened, papers are forcibly discharged to the discharge port even if the in-body tray is designated as a paper discharging destination.
If the in-body tray is designated as the paper discharging destination, a paper of small size, which cannot be discharged to the in-body tray because of hardware restriction, is discharged instead to the discharge port on the conveyance path.
However, there may be problems when a finisher is mounted to execute stapling operation. For example, when a paper, before being stapled, is discharged to the discharge port on the conveyance path if the discharge port is opened, or when a paper that is printed only on one side, but not on two sides, is output to the discharge port when the discharge port is opened during a double-sided printing, or when papers which can only be output to the discharge port on the conveyance path are printed, a jam may occur if the papers are forcibly output when the discharge port is closed.